Fluorescent lamp stand

For UV exposure of PCBs I bought a UV tube. It is no professional modell, more a party thing, but it works. I needed a stand to give me the right distance. I had a 12mm alu tube at hand, so the construction is for that size. There are holes to secure the tubes, but with my printer they stuck very well without help. A M6 screw nut is inserted in the parts to fix the holder.
For my usage (~14cm distance) a 25cm tube is right, which conveniently fits exactly 4 times in a 1m tube part. The tube fi